At first, I thought this case might be similar to the recent incident involving the Reflecting Pool on the National Mall in Washington D.C.
After a massive two-year renovation, as soon as the pool was filled it quickly filled with green algae.

Carol Johnson, a spokeswoman with the National Park Service, said officials had made attempts in the past week to remove the algae, which began showing up in the pool about a week after its reopening. Johnson had said earlier that the Park Service expected a “break-in period” for the pool, but no one had anticipated the amount of algae that appeared.

However, a quick search through the less-than-user-friendly archive on Omaha.com showed an article this past spring about the Gene Leahy Mall renovation project. That article also parroted the phrase "algae-invested lagoon".

... grant money from the Nebraska Environmental Trust will be spent to dredge and deepen the park's algae-infested lagoon...

Apparently the green algae present in Central Park Mall isn't exactly a sudden occurrence, as it was in the nation's capital. There is a more general dislike for the "green slime" present in the water.
I am not trying to say that the particular algae in the water in Central Park Mall is particularly beneficial. As my mother taught me when I was young, "A weed is any plant growing in a place where it isn't wanted. Even a rose is a weed if it's growing in the middle of the lawn"

Hopefully, news stories about the positive potential of algae as a source for biofuel will start showing up in the news soon. Then the mental association between "algae" and "ewwww" might start to shift. Keep your eyes open, those stories might even start to involve yours truly.